On a crisp morning in mid-December, plants and grass lay flattened on either side of Johnson Creek, hinting at recent floods.
Metro has been doing a lot of work in parks and natural areas, such as those along Johnson Creek, to protect wetlands and reconnect rivers and streams to their floodplains. These wetlands and floodplains absorb excess rainfall, which can help prevent flooding downstream, and also provide habitat for fish, birds and wildlife.
Though some of Metro’s restoration projects are small, they can collectively make a large impact in an ecosystem, especially in combination with projects done by other local agencies and partners.
“The importance of this (work) is that it allows the upper watershed to store more water in high-flow events,” said Kate Holleran, a senior natural resources scientist at Metro. “It stores water here, and it slows down the delivery of water (downstream).”
Reconnecting floodplains, side channels
Thanks to the voter-approved natural areas bond measures in 1995 and 2006, Metro has acquired more than 100 acres along Johnson Creek, including more than 9,300 feet of stream bank. Metro is actively restoring several sites, including work to reconnect the creek to its floodplain.
How does a river reconnect with a floodplain and what does that even mean?
Floodplains are the areas of land near a river that water can spill onto in times of heavy rain. These areas then soak up the water and hold it, so it doesn’t rush downriver and cause flooding.
The first step of restoration requires removing the human marks on the landscape.
At several sites along Johnson Creek, Metro has removed houses, barns and septic systems that were built in the floodplain decades ago.
It’s important to remove these structures because ground with natural vegetation can absorb a lot more water than ground covered in cement or gravel.
Another good way to spread the water out and slow it down is by reconnecting side channels to the stream, Holleran said. Side channels are smaller streams that break away from the main creek and reconnect a little later.
Reconnecting one of Johnson Creek’s side channels didn’t take much more than a day’s work, Holleran said while walking along the creek. An excavator dug out sediment that had blocked the flow of water into the side channel. After that, a log jam – built with large trees and boulders – was placed near the entrance of the side channel to direct more water into it.
Log jams, such as the many installed throughout Johnson Creek, also slow the water and catch sediment, which improves water quality.
Without healthy side channels and log jams, Johnson Creek would flow even faster. Over time, the fast-moving waters would carve deeper into the ground. A deeper creek means the water would be too far below the banks to access the floodplain. The sediment caught by the log jams helps to build the creek bed back up.
When water does rise high enough to flow into the floodplain, native trees slow water down, and their roots drink it up. The trees that do best in floodplains, such as willows, Douglas firs, Western red cedars and dogwoods, offer deep, extensive root systems.
Creating fish habitat
For the salmon that live and breed in the creek, slower waters are more than convenient – they are essential. Fast flows stress them, but side channels serve as places of refuge.
“When they want to get out of the high flow, they can go back into the side channel and hang out there for a little bit,” Holleran said.
Sediment trapped by log jams settles on the bottom of the creek. The uneven creek floor provides some deeper, cooler spots where fish can find refuge from warm waters and predators.
Reconnecting the floodplains provides fish access to new areas to find food, said Peter Guillozet, a senior natural resources scientist at Metro.
“They eat on these floodplains,” Guillozet said. “They get out and forage during high water, and they eat the insects that live in the vegetation. These are very important areas for fish, for fattening them up.”
At nearly 2,000 acres, Smith and Bybee Wetlands Natural Area in North Portland is able to hold a large amount of water during heavy rains.
One-way flaps at Smith and Bybee’s water control structure allow water to travel in, but Metro is able to control the release of water, slowly releasing it so that it doesn’t overwhelm downstream areas.
“In wetlands, the water gets soaked up and filtered through vegetation so it exits more slowly, which also helps with the recovery from flood events for other places,” said Elaine Stewart, a senior natural resources scientist at Metro who has worked at Smith and Bybee for 15 years.
Wetlands also trap silt and debris, which improves water quality.
The water control structure allows Metro to better simulate the natural processes that took place at Smith and Bybee before the surrounding industrial area developed.
The wetlands used to flood each spring, so the site’s native shrubs and trees, such as Oregon ash trees, are specially adapted to not grow until early summer. Without that spring flooding, invasive plants such as reed canarygrass take root and cover the ground before native plants have a chance to grow.
The water control structure allows winter rainwater to be held throughout the spring, preventing the growth of invasive species. The water’s slow release creates mud flats, perfect hunting grounds for sandpipers, yellowlegs and other shorebirds.
“These areas where the water has moved away that are not completely dry yet are where emergent plants grow, and also where shorebirds can walk around and stick their beaks down in there and eat little bugs that are living in the mud,” Stewart said.
Smith and Bybee’s water control structure is just one of the many ways Metro is working to restore natural processes and ecological features to the region’s parks and natural areas.
“In this system, the process that was broken was the hydrology, the water movement,” Stewart said. “With the water control structure, we’ve fixed that hydrology. We’re imitating the natural processes, and that sets it up to heal itself.”